1. Field of the Invention
The present invention relates generally to electric vehicle charging systems. The present invention relates particularly to induction coil based electric vehicle charging systems for parked vehicles or other stationary objects.
2. Discussion of Related Art
Induction charging of electric vehicles has been proposed in the art. In an induction charging system a primary coil induces a magnetic field into a secondary coil which produces a current subsequently used by on-board electronics of the electric vehicle to charge its batteries. While induction charging can offer advantages over other charging formats, one inescapable limitation of induction charging systems is that efficiency of the systems is very dependent upon proximity of the coils to each other, i.e. the gap distance. Less than two inches of gap is considered efficacious for a through-air proximity distance to achieve over 90% efficiency in induction charging. Efficiency drops off from the optimal with gap distances over two inches.
Some induction charging systems have been proposed for moving vehicles such as in U.S. Pat. No. 3,914,562. Some induction charging systems have been proposed for parked vehicles such as in U.S. Pat. Nos. 5,498,948 or 5,710,502.